Select the correct statement$($s$)$ regarding crosstalk interference on ADSL.

a$.$ FEXT is of greater concern over NEXT to service providers

b$.$ ADSL provides asymmetric data paths, therefore neither NEXT nor FEXT are of concern to service providers

c$.$ Service providers must ensure a proper ACR ratio to avoid NEXT or FEXT interference

d$.$ Since FDD is used on ADSL, crosstalk issues are not possible